Adjustable electromagnetic pick-up for stringed musical instruments



United States Patent Inventor James H. Rickard Harwinton, ConnecticutAppl. No. 815,612

Filed April 14, 1969 Patented Oct. 27, 1970 Assignee Kaman CorporationBloomfield, Connecticut a corporation of Connecticut ADJUSTABLEELECTROMAGNETIC PICK-UP FOR STRINGED MUSICAL [56] References CitedUNITED STATES PATENTS 1 2,612,072 9/1952 De Armond 84/1. 15 2,612,5419/1952 De Armond 84/1.15X

Primary Examiner-W. E. Ray Attorney-Mc Corrnick, Paulding & HuberABSTRACT: An electrical pickup for stringed musical instruments includesa plurality of magnetic cores adapted to be placed near the strings sothat the vibration of a string induces a varying flux through itsassociated core. A generating winding surrounds all of the cores and haselectrical signals induced therein by the varying fluxes through thevarious cores. The cores are adjustable to vary the spacing between themand the strings and a case providing a magnetic shield surroundsthe coiland cores. The construction of the adjustment means and of the case issuch as to prevent the production of extraneous circulating currentsopposing the flux variations, and to also allow the generating coil tobe positioned in very close proximity to the magnet cores, therebyenhancing the signal produced by the generating coil.

Patented Oct. 27, 1970 Sheet INVENIOR. JAMES H. RIGKARD 4% ATTORNEYSADJUSTABLE ELECTROMAGNETIC PICK-UP FOR STRINGED MUSICAL INSTRUMENTSBACKGROUND OF THE INVENTION This invention relates to transducers,commonly referred to as electrical pickups, for use with stringedmusical instru ments, such as guitars, banjos and-the like forconverting the vibrations of the instrument strings into electricalsignals which may be amplified and played back through a speaker orspeaker system to produce an amplified version of the sound produced bythe vibrating strings. More particularly, the invention relates to anelectrical pickup of the type employing a plurality of permanent magnetcores, one for each string or set of strings, surrounded by a commongenerating coil.

The general object of this invention is to provide an improvedelectrical pickup of the foregoing character and more particularly toprovide such a pickup which is of simple construction, convenient touse, easy to adjust and which is capable of producing an output signalof increased intensity in comparison to other such devices presentlyavailable so as to require a lesser degree of amplification to produce agiven intensity of sound from the associated speaker or speaker system.

SUMMARY OF THE INVENTION The invention resides in an electrical pickupfor stringed musical instruments such as guitars, banjos and the likeand consists of a plurality of permanent magnet cores which are normallyof such a number as to provide one such core for each string of theinstrument. The cores are received in a nonmagnetic, electricallynonconductive supporting body, located below the strings, which alsosupports a common generating winding surrounding all of the cores. Thecores project upwardly so as to have their upper ends positioned closeto the associated strings and when a string vibrates a varying flux isproduced through the associated core and induces a corresponding signalin the generating coil. The lower ends of the cores project through andbeyond the bottom of the support body and each includes a radiallyextending nonmagnetic adjustment arm fixed thereto which extends beyondthe outer edge of the coil. A nonmagnetic adjustment screw engagablewith the support body and the adjustment arm is also located beyond theouter edge of the coil thereby allowing the coil to pass in closeproximity to the magnet cores without the interposition of any part ofthe adjustment means. An electrically conductive case forming anelectric shield surrounds a major portion of the generating coil and hasupper and lower openings through which the upper and lower ends of themagnet cores pass. A gap in this case extending from the upper openingto the bottom opening provides a nonconductive zone in the case so as topresent an open circuit to electrical currents which would otherwisecirculate through the case about the axis of the generating coil andoppose the varying flux passing through the magnet cores, thereby makinga greater degree of flux change available for generating an outputsignal in the generating coil and increasing the intensity of suchsignal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of aguitar utilizing two electrical pickups embodying this invention.

FIG. 2 is a perspective view of one of the electrical pickups of theFIG. 1 guitar.

FIG. 3 is another perspective view of the electrical pickup of FIG. 2,but taken at a different angle.

FIG. 4 is still another perspective view of the pickup of FIG. 2, buttaken at still another angle.

FIG. 5 is an enlarged top view of the pickup of FIG. 2.

FIG. 6 is a transverse sectional view taken on the line 6-6 of FIG. 5.

FIG. 7 is a view partly in section and partly in elevation taken on theline 7-7 of FIG. 5.

DESCRIPTION THE PREFERRED EMBODIMENTS Turning to the drawings, FIG. 1illustrates, by way of-an example, a guitar 10 having two electricalpickups l2 and 14 embodying this invention. Both of the pickups 12 and14 are mounted in openings formed in the top of the guitar body and arelocated below its strings l6, 16. The pickup 12 is located near thelower end of the finger board 18 of the guitar and is intended to pickup the fundamental and, lower harmonics of the string vibrations. Thepickup 14, on the other hand, is located near the bridge 20 and isintended to pick up the higher harmonics of the string vibrations.Although desirable for best performance, it is not, however, entirelynecessary to have two pickups on the guitar and in some cases guitarsand other instruments may be made including only one such pickup.

As explained in more detail hereinafter, and still referring to FIG. 1,each of the pickups l2 and 14 includes a plurality of permanent magnetcores 22, 22 each of which is associated with a respective one of thestrings l6, 16, there being six strings in the illustrated guitar and acorresponding set of six cores 22, 22 in each of the pickups. In somecases, such as twelve stringed guitars, mandolins and other instrumentsusing closely spaced pairs of strings tuned in unison, a single core 22may sometimes be used with each such pair of strings, but even in theseinstruments it is usually desirable to have a separate core 22 for eachstring.

The two electrical pickups l2 and 14 of FIG. I are identical to eachother except for pole spacing and, for the purpose of illustration,FIGS. 2 to 7 show the detailed construction of one of these units whichmay be taken to be the upper unit 12. Turning to FIGS. 2 to 7, thepickup 12 there shown comprises a base or support body 24 which is madeof a nonmagnetic and electrically nonconductive material such asplastic. The support body 24 may be made as a unitary piece, butpreferably and as shown best in FIGS. 6 and 7, for ease of manufactureis made in two parts, these parts being a molded upper part 26 and abottom plate 28. The support body 24 includes a longitudinally extendingcentral portion 30 provided with a plurality of openings 32, 32 whichpass therethrough from the top surface 34 of the body to the bottomsurface 36. Each of the holes 32 in turn slidably receives a generallycylindrical permanent magnet core 22 made of alnico or the like andhaving an upper end portion which normally projects upwardly beyond thetop surface 34 and a lower end portion which normally projectsdownwardly beyond the bottom surface 36.

The support body, as best shown in FIG. 6 also includes, on either sideof the central portion 30, an upper flange 38 and a lower flange 40, thelower flange 40 in the illustrated case being formed by the bottom plate28. The top and bottom flanges 38 and 40 are spaced from one anotheraxially of the magnet cores 22, 22 and receive therebetween a generatingwinding 42 consisting of many turns of fine wire wound around thecentral portion 30 so as to surround in common all of the magnetic cores22, 22, the shape of the central portion 30 giving the coil an elongatedconfiguration with one elongated portion located on one side of thecentral portion and another elongated portion located on the other sideof the central portion.

Each of the magnetic cores 22, 22 of the pickup 12 is adjustable alongits axis relative to the support body 24 independently of the othercoresto vary the spacing between its upper end face and the associatedstring 16. As a means for accomplishing this adjustment, each magnetcore 22 has an adjustment arm 44 of nonmagnetic material fixed to itslower end portion. The arm44 extends radially of the associated core 22to one side of the center portion 30 of the support body and to apointspaced beyond the outer edge 46 of the adjacent elongated portion of thecoil 40, as shown best in FIG. 6. On this same side of the centralportion 30 the upper flange 38 and bottom flange40 of the support memberalso extend beyond the outer edge 46 of the coil and for each adjustmentarm 44 include an opening 48 in the upper flange and an aligned opening50 in the bottom flange. The two openings 48 and 50 associated with eachadjustment arm 44 receive an adjusting screw 52 which is threadablyconnected with the outer end of the adjustment arm 44. The upper opening48 is counterbored to receive the head of the screw and to provide abearing surface for engaging its undersurface. A helical compressionspring 54 of nonmagnetic material is received on the screw 52 I and ispositioned with its upper end in engagement with the top flange 38 andwith itslower end inengagement with the adjustment arm 44, the spring 54and screw 52 passing loosely through the bottom opening 50. The spring54, therefore, urges the adjustment arm 44 and attached core 22downwardly relative to the support body 24 and by turning the screw bymeans of a tool placed in the slot of its head, the adjustment ann maybe moved to different axial positions relative to the screw to changethe position of the core relative to the support body and totheassociated string.

Before dismissing consideration of the adjustment means, it should benoted that the arrangement of the various parts of the adjustmentmechanism as shown in FIGS. 6 and 7 allows the adjusting screw 52 andthe spring 54 to be located beyond the outer edge of the generating coil42 and allows the generating coil to be located in very close proximityto the magnet cores 22, 22 thereby providing the closest possible fluxlinkage between the coil and the varying flux passing through the cores.Also, the springs 54, 54 are received on the screws 52, 52, rather thanon the cores 22, 22 and, therefore, have no influence on the flux. Ifthe springs were placed on the magnet cores 22, 22, they could act asshorting windings providing a path for electrical currents opposing theflux changes occurring in the magnet cores.

Surrounding the major portion of the support body 24 of the pickup 12 isa case 56 of electrically conductive nonmagnetic material which inaddition to its serving as a mechanical housing or cover, also serves toprovide an electric shield which shields the coil 42 against strayelectric fields in the air which would otherwise be picked up andproduce hum or other noise in the speakers. In the illustrated case, thecase 56 is made of two parts comprising a generally cup-shaped uppermember 58 and a bottom plate 60 both of which are preferably made ofbrass. As shown in FIGS. 3 and 4, the bottom plate 60 fits within thelower edge of the cup-shaped upper member 54 and is fixed thereto bysolder applied at various points along the adjoining edges of the twoparts as indicated at 62, 62 in FIGS. 3 and 4. At each end of the pickupthe bottom plate 60 projects beyond the adjacent edge of the member 58and is apertured to provide mounting ears 64, 64.

The case 56 adjacent the upper surface 34 of the support member 24includes a relatively large opening 66 generally centered with the axisof the generating coil 42 and through which opening the upper ends ofthe magnet cores 22, 22 project. Likewise, the bottom of the case 56includes a relatively large bottom opening 70, but smaller than the topopening 66, also generally aligned with the axis of the coil and throughwhich the lower end portions of the cores 22, 22 project. Other smalleropenings 72, 72 are also formed in the bottom of the case foraccommodating the adjustment screws 52, 52 and their associated springs54, 54 and in the upper surface of the case other small openings 74, 74are provided in registration with the heads of the adjustment screws toallow access to such heads by a screwdriver for rotating the same whenmaking an adjustment.

In considering the case 56, it should be noted that it constitutes apiece of electrically conductive material surrounding the axis of thecoil 42 and the magnet cores 22, 22, and, there fore, if it were acontinuous piece of material it would provide a closed circuit forcirculating electrical currents opposing the variations in flux passingthrough the cores 22, 22. In order to prevent such circulating currentsand to thereby increase the intensity of the output signal produced bythe generating coil,

the case 56 at one point there along includes a nonconductive zoneextending from its upper opening 66 to its lower opening 70. In theillustrated case, this nonconductive zone is formed by a gap 76 in thecase, including both the top part 58 and bottom plate 60 thereof,extending from-the top opening 66 to the bottom opening 70. This gap 76,therefore, presents an open circuit to electrical currents which wouldotherwise circulate about the axis of the coil and around the magneticcores 22, 22 and, as explained, permits greater variations in the fluxthrough the magnet cores and as a result of this provides a greaterintensity of output signal from the generating coil.

Iclaim:

1. A pickup for stringed musical instruments, said pickup comprising asupport body of nonmagnetic and electrically nonconductive materialhaving a top surface and a bottom surface and a longitudinally extendingportion provided with a plurality of longitudinally spaced r: parallelholes extending therethrough from said top surface to said bottomsurface, a plurality of permanent magnet cores each received in arespective one of said holes, a generating coil wound around saidlongitudinally extending body portion with its axis generally parallelto said holes so as to surround saidplurality of permanent magnet cores,and a shielding case of electrically conductive material surroundingsaid support body and said coil, said case having a top openinggenerally centered with the axis of said coil and a bottom opening alsogenerally centered with the axis of said coil, arid said case furtherhaving at one point there along a nonconductive zone extending from theedge of said upper opening to the edge of said lower opening so as topresent an open circuit for electrical currents which would otherwisecirculate through said case about the axis of said coil.

2. A pickup for stringed musical instruments as defined in claim 1further characterized by said permanent magnet cores each having a topend portion extending above said top surface and a bottom end portionextending below 'said bottom surface, said upper opening of said casereceiving and surrounding said upper end portions of said magnetic coresand said lower openings of said case receiving and surrounding saidlower end portions of said cores.

3. A pickup for stringed musicalinstruments as defined in claim 1further characterized by said nonconductive zone of said case beingdefined by a gap in the material of said case which gap extends from theedge of said upper opening to the edge of said lower opening. I

4. A pickup for stringed musicalinstruments as defined in claim Ifurther characterized by each of said permanent magnet cores beingslidably received in its respective hole of said support body, and anadjustment means associated with each of said cores for adjusting thesame along its axis relative to said body to vary the amount by whichthe upper end thereof projects beyond said upper surface of said body.

5. A pickup for stringed musical instruments as defined in claim 4further characterized by said adjustment means for each of said corescomprising an arm attached to the lower end portion of said core beyondsaid support body and coil and extending radially to a point beyond theouter edge of said coil, and an adjustment screw carried by said supportbody and threadably engaged with said arm, said screw being locatedbeyond said outer edge of said coil.

6. A pickup for stringed musical instruments as defined in claim 5further characterized by said support body including axially spaced,generally radially extending upper and lower flanges between which saidgenerating coil is received, said generating coil including twoelongated portions each extending along one side of said longitudinalportion 'of said support body, said upper and lower flangesof saidsupport body along One of said elongated portions extending radiallyoutwardly beyond said coil portion, and having axially aligned openingsfor receiving said adjustment screw, said opening in the upper flangeincluding a seat for engagement with the head of said adjustment screwand said adjustment screw passing loosely through the opening in saidbottom flange, and a helical spring received on said screw and workingbetween said arm and said support body for urging said screw and saidmagnetic core downwardly relative to said support body.

7. A pickup for stringed musical instruments as defined in claim 6further characterized by said spring passing loosely through saidopening in said bottom flange and engaging said upper flange.

8. A pickup for stringed musical instruments as defined in claim 7further characterized by each of said openings in said upper flangebeing recessed to receive the head of the associated adjustment screwand said case including a portion which adjacent said top surface ofsaid support body extends generally over the area of said upper flangecontaining said adjustment screw openings, said case portion includingindividual openings each aligned with a respective one of said screwsfor providing access to the associated screw head for adjustmentpurposes.

9. A pickup for stringed musical instruments, said pickup comprising asupport body of nonmagnetic and electrically nonconductive materialhaving a top surface and a bottom surface and a longitudinally extendingportion provided with a plurality of longitudinally spaced parallelholes extending therethrough from said top surface to said bottomsurface, a plurality of permanent magnet cores each slidably received ina respective one of said holes and having a top end portion extendingabove said top surface and a bottom end portion extending below saidbottom surface, a generating coil wound around said longitudinallyextending body portion with its axis generally parallel to said holestherein so as to surround said plurality of permanent magnet cores, ashielding case of electrically conductive material surrounding saidsupport body and said coil, said case having a top opening through whichsaid top end portions of said magnetic cores extend and a bottom openingthrough which said bottom end portions of said magnetic cores extend,and a plurality of means each associated with a respective one of saidcores for adjusting the associated core along its axis relative to saidsupport body to vary the extent by which its upper end portion projectsabove said top surface of said support body, each of said adjustmentmeans including an adjustment arm of nonmagnetic material fixed to thelower end portion of the associated magnetic core below said case andextending radially of said core to a point located beyond the outer edgeof said generating coil, and an adjustment screw located beyond saidouter edge of said generating coil and engaged with said support bodyand said adjustment arm for moving said adjustment arm relative to saidbody.

10. A pickup for stringed musical instruments as defined in claim 9further characterized by said support body including axially spaced,generally radially extending'upper and lower flanges between which saidgenerating coil is received, said generating coil including twoelongated portions each extending along one side of said longitudinalportion of said support body, said upper and lower flanges of saidsupport body along one of said elongated portions extending radiallyoutwardly beyond said coil portion and having axially aligned openingsfor receiving said adjustment screw, said opening in the upper flangeincluding a seat for engagement with the head of said adjustment screwand said adjustment screw passing loosely through the openings in saidbottom flange, and a helical spring received on said screw and workingbetween said arm and support body for urging said screw and saidmagnetic core downwardly relative to said support body.

11. A pickup for stringed musical instruments as defined in claim 10further characterized by said spring passing loosely through saidopening in said bottom flange and engaging said upper flange.

12. A pickup for stringed musical instruments as defined in claim 11further characterized by each of said openings in said upper flangebeing recessed to receive the head of the associated adjustment screw,and said case including a portion which adjacent said top surface ofsaid support body extends generally over the area of said upper flangecontaining said adjustment screw openings. said case portion includingindividual openings each aligned with a respective one of said screwsfor providing access to the associated screw head for adjustmentpurposes.

